The present invention relates to a socket joint for two pipeline elements, in which the spigot end of one pipeline element is inserted in the socket end of the other pipeline element and is sealed by an elastomeric gasket. As a thrust or shear preventer the outer circumference of one pipeline element is embraced by a retaining ring on which is supported a thrust or shear preventing ring, which is fixed to the socket other end of the other pipeline element.
The socket joint is a known and frequently used pipe connection or coupling, which is in particular used in the case of cast pressure pipes, shaped parts and fittings and which has proved satisfactory under difficult operating conditions. However, the socket joint suffers from the disadvantage that it is unable to absorb axially directed forces, so that additional anchoring means must be used for such an application.
It is further known to construct the socket joint in such a way that it can absorb axial forces. These additional means are called a thrust preventer and various constructions thereof are known. In one construction (Swiss Pat. No. 622 597 and German Pat. No. 21 62 435), the thrust preventer essentially comprises a retaining ring and a thrust preventing ring. The retaining ring is placed on the spigot end of one pipeline element and is provided on its inner circumference with a tooth system ensuring the non-positive engagement of the spigot end of one pipeline element via retaining and thrust preventing rings on the other pipeline element. In another construction, the inner circumference of the surface is smooth and a bead located at the spigot end permits the non-positive engagement of the latter on the retaining ring. The outer circumference of the retaining ring is constructed as a spherical zone, on which is supported the spherically constructed inner surface of the thrust preventing ring, which is connected to the socket end, e.g. by retaining claws.
Both constructions suffer from significant disadvantages. The unprotected teeth are exposed to corrosion. There is the fundamental risk of the operational reliability of the thrust preventer being prejudiced in the case of corroded tooth tips. In addition, the spigot end surface damaged by the action of the teeth is also exposed to corrosion. Thus, the life of the particular pipeline element is considerably reduced.
The fitting of a bead involves additional work and requires additional material. When carried out on the site, as is often the case when producing so-called short and fit lengths, this considerably increases costs. In addition, the quality is reduced. Excessive penetration of the bead, structural changes in the material and a destruction of the corrosion-resistant skin lead to the weakening of the pipeline element.
In another known construction (Swiss Pat. No. 569 913), the retaining ring is replaced by wedge-shaped retaining segments, which are inserted in recesses at the socket end, screw or pressure ring and by means of hammer blows moved into an area of the recesses with a smaller passage, so that a key joint is obtained.
All three constructions suffer from the aforementioned disadvantage with respect to the corrosion of the unprotected teeth. The construction with the recesses at the socket end involves a modification of all the socket core bushes required for producing the pipeline elements.
The construction with recesses on the screw and pressure ring require a modification to the corresponding molding equipment. Apart from a relative stiffening of the screw and gland-type socket joint, the disadvantage occurs that the functional requirements made on a socket joint by the prior art with respect to sealing and longitudinal non-positive engagement have to be overcome in two independent systems.
In another known construction (U.S. Pat. No. 4,330,143) the width of the retaining ring is greater than the pipe diameter, to prevent sliding of the spigot end when axial forces occur. However, this leads to a very considerable overall height, so that the thrust preventing ring is constructed as a flange and a similar flange is supported at the socket end. The thrust preventing ring is connected to the socket end flange by means of screw bolts. This construction is too complicated and expensive for most uses. Another disadvantage is the considerable stiffening of the joint, so that it can only be considered for special applications.